Some communication systems use an adaptive array antenna method to control a directionality of an array antenna comprising multiple antennas. A base station can transmit signals to a destination mobile phone via an adaptive array antenna so as to mitigate interference with other mobile phones. The base station forms antenna beams (beam forming) from the adaptive array antenna to direct transmission signals to the destination mobile phone during transmission.
The antenna beams are formed based on known-received signals from the mobile phone. If the timing in which the known signals are received and the timing in which the signals are transmitted by performing beam forming based on the known-received signals are distant from each other, an accuracy of the beam forming decreases at the base station. As a result, interference can be caused at other mobile phones.